Safety system



F. M. BECK SAFETY SYSTEM June 22, I943.

Filed Jan. 29

Inventor: Francis M. Beck,

H Attorney Paitented June 22, 1943 SAFETY SYSTEM Francis M. Beck, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application January 29, 1942, Serial No. 428,737

12 Claims.

My invention relates to safety systems and particularly to safety systems of the interlocked control type requiring the operation of each of a plurality of separate control devices in order to energize a controlled element. 7

In many applications of industrial machinery such as punch presses, welders and the like, it is desirable, in order to minimize the danger of injury to the operator, to so design the machine control that both hands of the operator are required to initiate operation. In this way it is impossible for an operator carelessly to set a machine in operation while he remains in a dangerous position.

My invention is also applicable to sequentially operating systems in which it is desired that each of a plurality of electrical or mechanical devices shall have operated, or shall have simultaneously operated, before a controlled element is energized.

Accordingly, it is an object of my invention to provide a safety system so interlocked that each of a plurality of control elements must be operated before a controlled element may be energized.

It is a further object of my invention to provide, in a safety system of the above character, means for deenergizing the controlled element upon release of any one of the control devices.

A still further object of my invention is to provide, in a safety system of the above character, means for deenergizing the controlled element after a predetermined interval of time regardless of the position of the control devices.

A still further object of my invention is to provide a safety system comprising interlocked control circuits so arranged that each of a plurality of independent control devices must be substantially simultaneously operated in order to produce energization of a controlled element.

According to one preferred modification of my invention a direct current relay, normally disabled by each of a plurality of control devices, is connected in shunt with a normally charged capacitor and is energized by the discharge of the capacitor. The control devices through which the relay is connected to the capacitor are so arranged that operation of any one of them will disable the charging circuit for the capacitor. In order to insure that the control devices are all substantially simultaneously operated, a discharge resistor might also be connected in parallel with the capacitor. Such a resistor will provide a discharge circuit for the capacitor upon operation of any one of the control devices, while the discharge circuit through the relay will not be completed until all the control devices have been operated.

Other objects and advantages of my invention will be apparent from the following description taken in conjunction with the accompanying drawing, and the features which I believe to be novel and patentable will be pointed out with particularity in the appended claims. In the drawings the various Figs. 1, 2, 3 and 4 are simplified circuit diagrams of various modifications of my invention. Corresponding elements of the various figures have been assigned like reference numerals.

Referring now to the drawing, I have indicated a unidirectional source of electric current supply by the positive and negative conductors I0 and II, respectively. It will be understood, of course, that while I contemplate a direct current supply source, the particular polarity indicated is not essential to the invention. A plurality of control elements, which I have shown for convenience as a pair of push buttons I2 and I3, are provided with normally closed contacts I4 and I5, respectively, and with normally open contacts I6 and II, respectively. Through the normally closed contacts I4 and I5 a charging circuit is normally completed for a capacitor I8. Through the normally open contacts I6 and II and suitable circuit connections an operating coil I9 of a control relay 20 is adapted to be connected in shunt with the capacitor I8. The control relay 20 is shown by way of example provided with a pair of control contacts 25 in a controlled circuit 26.

While I have shown the control devices I2 and I3 as push buttons, I wish to have it understood that, if desired, the devices I2 and I3 may be either manually or automatically operated, and, if automatically operated, that they may be operated either electrically or mechanically. Furthermore, while I have shown the controlled element 20 as a relay having a single pair of contacts 25, it will be understood by those skilled in the art that the element 20 may perform any desired mechanical or electrical control functions.

Referring now to Fig. 4, the operation of the system therein illustrated is as follows: Normally the push buttons I2 and I3 are biased to the position shown. In this position a charging circuit for the condenser I8 is completed through the contacts I4 and I5 and the operating coil I9 of the relay 20 is disabled at the contacts I6 and II. If now, both push buttons I2 and I3 are depresed in any desired order and with any desired interval of time between the operation of the various buttons, the condenser I8 will be disconnected from the line conductors I and II' and the operating coil III will be connected across the condenser to provide a discharge path therefor. The discharge of the condenser I8 through the operating coil I9 will energize the relay 20 and will hold it picked up for a predetermined period of time determined by the capacity of the condenser I8 and the resistance of the coil I9. When the condenser discharge current has diminished to a value insuificient to hold the relay 20 operated, the relay will drop out. If, however, before the discharge current has diminished to this value, either one of the push buttons is released, the energizing circuit for the operating coil I9 will be broken, although the charging circuit for the condenser I8 will not be reestablished until both push buttons are released. Thus, the push buttons I2 and I3 jointly control the operating coil I9.

Referring now to Fig. 1, I have shown another modification of my invention having all the elements of Fig. 4 and, in addition, a discharge resistor 21 permanently shunting the condenser I8. The efiect of the resistor 2'! is to permit operation of the relay 2!! only if both push buttons I2 and I3 are operated substantially simultaneously. To illustrate, let it be assumed that only one push button, for example, the push button I3, is depressed. Under such conditions the charging circuit for the condenser I3 will have been disabled at the contacts I5 of the push button I3; and, although the contacts II in circuit with the operating coil I9 will have been closed, the energizing circuit for the coil I9 will still be incomplete because of the failure to close the contacts I6 of the push button I2. So long as this condition persists, the condenser I8, having its charging circuit disabled, will discharge through the permanently connected shunt resistor 21. If, after the capacitor I8 has discharged through the resistor 21, the push button I2 is depressed, no energization will be applied to the operating coil I9 of the relay 2!), since no potential difference will remain upon the capacitor. On the other hand, however, if the push buttons I2 and I3 are depressed substantially simultaneously, an energizing circuit will be completed for the operating coil I 9 of the relay before the capacitor I8 has had time to discharge through the resistor 21. In this case two shunt circuits will exist across the capacitor I8, namely, a circuit through the discharge resistor 21 and a circuit through the operating coil IS. The discharge current of the condenser I8 will therefore divide through the resistor and the operating coil. It will be understood, of course, that the resistance of the resistor 21 must be sufficiently great, relative to the resistance of the operating coil I9, to permit an adequate operating current to pass through the operating coil Iii.

In Fig. 2 I have shown another modification of my invention similar to that shown in Fig. 1, with the addition that a pair of normally closed contacts 28 on the relay 2!] are connected in the charging circuit of the capacitor IS. The provision of the contacts 28 insures that the relay 20 is completely deenergized after one operation before another operation may be initiated. It will be apparent that this effect arises from the fact that the condenser I8 cannot be recharged until the relay 20 has been completely deenergized.

In the modifications of my invention according to the Figs. 1, 2 and 4 the period during which the relay 20 remains picked up is ordinarily determined by the charge upon the capacitor I3 and the resistance of its discharge circuit. In each of these modifications, however, if any one of the push buttons is released prior to the expiration of this predetermined period, the energizing circuit for the operating coil I9 will be immediately disabled, as has already been de-' scribed with reference to Fig. 4.

In order to insure that the relay 23 will remain picked up for the full period determined by the charge on the condenser I8, use may be made of the modification of my invention illustrated in Fig. 3. It will be observed that the modification of Fig. 3 is substantially similar to that of Fig. 2, with only the addition of a pair of normally open contacts 29 on the relay 2Il The contacts, 29 are so connected that when closed they complete a shunt circuit around the contacts I6 and ll. of the push buttons I2 and I3 respectively. The contacts 29 of the relay 20 therefore complete a locking-in circuit for the relay 20 and free it from the control of the contacts I5 and Il after its operation.

In Figs. 2 and 3 the discharge circuit for the condenser I8 passes through the relay winding I9 and the resistor 21 in parallel when all the push buttons are actuated substantially simultaneously. If desired the parallel circuit through the resistor 21 may be disabled from actuation of the relay by connecting in the resistor circuit a pair of normally closed contacts on the relay 29, such as the contacts 30 illustrated at Fig. 3.

While I have described only certain preferred forms of my invention, many other modifications and applications will occur to those skilled in the art; and I, therefore, wish to have it understood that in the appended claims I intend to cover all such modifications and applications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric safety control system for timing an operation comprising controlled electro-responsive means, time element energizing means for said electro-responsive means, and a plurality of independent switching means arranged jointly to control said electro-responsive means, said switching means having contacts arranged normally to connect said time element energizing means to a source of electric supply and upon actuation of all said switching means to connect said electro-responsive means to said time element energizing means and to disconnect said energizing means from said source.

2. An electric safety control system for timing an operation comprising a condenser, a relay, a plurality of separate switching means having normally open contacts arranged upon actuation jointly to connect said condenser in shunt with said relay, and contacts associated with at least one of said switching means for normally connecting said condenser to a source of electric supply.

3. An electric safety control system for timing an operation comprising a condenser, a plurality of push buttons having normally closed contacts connected in series and to said condenser to complete a charging circuit for said condenser, a re lay, and normally open contacts carried by said push buttons and connected in series circuit relation to connect said relay in shunt with said condenser when said charging circuit is disabled.

4. An electric safety control system for timing an operation comprising controlled electr0-re sponsive means, time element energizing means for said electro-responsive means, a plurality of independent control means arranged jointly to connect said electro-responsive means to said energizing means, and means operative upon delayed actuation of at least one of said control means to disable said energizing means thereby to permit actuation of said electro-responsive means only upon substantially simultaneous actuation of said control means.

5. An electric safety control system for timing an operation comprising a condenser, a relay, a resistor connected in shunt with said condenser, a plurality of independently operable switching means having normally open contacts arranged upon actuation jointly to connect said relay in shunt with said condenser, and contact means associated with said switching means for normally connecting said condenser to a source of electric supply.

6. An electric safety control system for timing an operation comprising a condenser, a resistor connected in shunt with said condenser, a plurality of push buttons having normally closed contacts connected in series and to said condenser to complete a charging circuit for said condenser, a relay, and normally open contacts carried by said push buttons and connected in series to connect said relay in shunt with said condenser when said charging circuit is disabled.

'7. An electric safety control system for timing an operation comprising a controlled electroresponsive device, time element energizing means for said device, a plurality of independently operable control means arranged jointly to connect said device to said energizing means, means associated with said electro-responsive device to control said energizing means, and means operative upon delayed actuation of at least one of said control means to disable said energizing means thereby to permit actuation of said electro-responsive device only upon substantially simultaneous actuation of said control means.

8. An electric safety control system for timing an operation comprising a condenser, a resistor connected in shunt with said condenser, a relay, a plurality of independently operable switching means, first contact means associated with said switching means jointly to connect said relay in shunt with said condenser, second contact means associated with said switching means to complete a charging circuit for said condenser, and third contact means associated with said relay to control said charging circuit.

six

9. An electric safety control system for timing an operation comprising a condenser, a resistor permanently connected in shunt with said condenser, a relay, a pluralityof push buttons, normally open contact means on said push buttons connected in series to complete a shunt circuit for said condenser through said relay, normally closed contact means on said push buttons connected in series and forming a part of a charging circuit for said condenser and normally closed contact means associated with said relay connected to complete said charging circuit.

10. An electric safety control system for timing an operation comprising a condenser, a resistor connected in shunt with said condenser, a relay, a plurality of independently operable switching means, first contact means associated with said switching means arranged jointly to connect said relay in shunt with said condenser, second contact means associated with said switching means arranged to complete a charging circuit for said condenser, and means associated with said relay for disabling said first contact means.

11. An electric safety control system for timing an operation comprising a condenser, a resistor connected in shunt with said condenser, a relay, a plurality of independently operable switching means, first contact means associated with said switching means and connected in series to complete a shunt circuit for said condenser including said relay, second contact means associated with said switching means and connected in series to complete a charging circuit for said condenser, and third contact means associated with said relay for shunting said first contact means of said relay.

12. An electric safety control system for timing an operation comprising a condenser, a resistor connected in shunt circuit with said condenser, a relay having a pair of normally closed contacts to control said shunt circuit, a plurality of independently operable push buttons, normally open contact means associated with said push buttons and connected in series to complete a discharge circuit for said condenser including said relay, normally closed contact means associated with said switching means and connected in series to form part of a charging circuit for said condenser, a second pair of normally closed contacts associated with said relay connected to complete said charging circuit, and a pair of normally open contacts associated with said relay and connected to shunt said normally open contact means after operation of said relay.

FRANCIS M. BECK. 

